The present invention relates to an improved extraction process for the deoiling of the products of the sulfonation of higher olefins. More particularly, the invention relates to improvements in such a process which are associated with the use of an alkane-based extraction solvent comprising a particular cosolvent.
It is well known to prepare valuable anionic surfactants by the sulfonation reaction between detergent range (e.g., C.sub.8 to C.sub.24) olefins and sulfonating agents such as sulfur trioxide. Olefin sulfonate products have found commercial utility in detergent formulations for industrial, household and personal care uses. Interest has recently been shown in their application in enhanced oil recovery processes.
In essentially all cases, the olefin sulfonation reaction does not accomplish complete conversion to the desired surface active sulfonate compounds (referred to as active matter), and the crude product contains a significant amount (e.g., 3 to 30%) of the unsulfonated olefin starting material (referred to as fee oil or neutral oil). Free oil represents a particularly objectionable impurity in the sulfonation product, from the standpoint of its influence upon detergency, foaming, color, odor and other physical and chemical properties.
Various processes have been proposed in the art to remove free oil from (i.e., to "deoil") olefin sulfonates and related anionic organic surfactants, both to improve product quality and to recover valuable olefin for recycle to the sulfonation reaction. As a general rule, such processes involve extraction of the free oil, using an extraction solvent which is based upon an alkane and which additionally contains a lesser amount of a cosolvent. Clear preference has been expressed in the prior art for a cosolvent which is a lower alkanol, most particularly isopropyl alcohol. For example, U.S. Pat. No. 4,322,367 describes processes for the extraction of oils from sulfates and other anionic detergents, using an extraction solvent which comprises both a C.sub.4 to C.sub.g hydrocarbon, most preferably hexane, and a C.sub.1 to C.sub.3 alcohol, most preferably isopropanol. According to that patent, related processes involving extraction systems containing hydrocarbon and/or alcohol solvents are described in U.S. Pat. No. 2,412,916, U.S. Pat. No. 2,655,530, U.S. Pat. No. 2,673,207, U.S. Pat. No. 2,687,420, and U.S. Pat. No. 3,941,810. It has also been found that U.S. Pat. No. 2,820,056, U.S. Pat. No. 3,444,191, U.S. Pat. No. 3,496,226, U.S. Pat. No, 3,842,095, U.S. Pat. No. 3,862,983, U.S. Pat. No. 4,197,255, and U.S. Pat. No. 4,318,823 each reports an extraction of an organic sulfonation product which involves a C.sub.4 to C.sub.9 alkane and/or a lower, water soluble alcohol solvent. U.S. Pat. No. 4,248,793 describes a similar extraction process employing a halogenated hydrocarbon solvent. U.S. Pat. No. 4,321,216 teaches a mixed deoiling extraction solvent comprising immiscible polar (e.g., carboxylic acid) and nonpolar (e.g., octane) components.
It is also common practice in the art to conduct analyses of the free or neutral oil content in organic sulfonation products by extraction with alkane and/or alcohol solvents. The publication by F. T. Weiss, A. E. O'Donnell, R. J. Shreve and E. D. Peters entitled "Comprehensive Analysis of Sodium Alkyl Aryl Sulfonate Detergents" "Analytical Chemistry, Vol. 27, No. 2, Feb. 1955, pp. 198-205) describes a separation of neutral oil from alkyl aryl sulfonates by extractions with petroleum ether (pentane) and isopropyl alcohol. ASTM Method D-3673 is directed to similar analytical procedures.
Although extraction processes utilizing alkane-based solvents containing alcohol cosolvents are recognized to be effective for the deoiling of organic sulfonates, they are typically not as efficient as would be desirable in this service. In general, conventional deoiling practices necessarily make use of relatively large quantities of solvent and/or of multiple extraction stages to reduce free oil content to the extent desired. It is the principal object of this invention to provide a process having improved efficiency for the deoiling of olefin sulfonates.
In one important respect, the present invention is directed to discoveries associated with the use of dimethyl ketone (acetone) as a cosolvent in an alkane-based solvent extraction process for the deoiling of olefin sulfonates.
In this regard, the prior art teaches only that under certain conditions, sulfonation products are soluble in acetone, alcohols, water, and the like. U.S. Pat. No. 2,243,332 discloses that sulfonation products may be applied (for instance, as detergents, emulsifiers, textile treating agents, tanning agents, mineral flotation agents, etc.) in the form of solutions in water, alcohol or acetone. U.S. Pat. No. 2,673,208 describes the extraction of an organic sulfonate from a mixture containing inorganic salts, which comprises treating the mixture with an organic solvent such as a lower alcohol, a fatty acid glycol ester, a ketone (including acetone, methylethyl ketone, diethyl ketone and their substituted derivatives) isobutyric acid, dioxane, and various ethers. U.S. Pat. No. 3,644,499 discloses a process for producing detergent sulfonates by reaction of an olefinic compound with an alkali bisulfate sulfonating agent, necessarily carried out in the presence of a reaction solvent containing both a polar solvent and an organic solvent such as a lower alcohol, a ketone such as acetone, methylethyl ketone, diethyl ketone, and diisobutyl ketone, tetrahydrofuran, and dimethylformamide. On the other hand, the examples of U.S. Pat. No. 3,487,104 describe a process for converting a sultone to an alkene sulfonate, wherein the product is purified by recrystallizations from methanol and washings with hot methyl ethyl ketone and dimethyl ketone, indicating that the sulfonate is soluble in methanol but not in the lower ketones.